IMAGINE an apartment dwell- er producing enough vegeta- bles on the balcony to get a couple through the summer. It can be done following the lessons of the U.S. Aboretum's National Country Garden. Here celery shares a clothesline with eggplant, tomatoes float free in a pool, and flowers and cabbage are neighbors growing out of Living Walls.

"The point of the garden is to show people how food can be grown in a small place," says Ed Toth, the garden's curator. But it goes further than that; the garden also demonstrates how fruit and vegetables can be raised in Washington three-quarters of the year, which varieties grow best when, that they can all be grown soil-free, and that urban gardening can be done at all income levels.

This, the most recent of 30 garden displays at the U.S. Aboretum in Northeast Washington, is planted in the middle of a three-acre site. Even so, Toth and local architects Guy L. Rando and Associates only used one acre to make their point. There are over 100,000 different plants (fruit, vegetable and flowering) growing in 13 outdoor "intensive" gardening rooms. They are handsomely landscaped along a path simulating specific urban settings. By next spring the periphery will be planted with dwarf apple, peach, nectarine and pear trees to protect early crops from the cold spring winds, Toth said.

Some of the plants are housed in materials found around a city, while other plants grow directly in bags of various growing mediums other than dirt. Still others grow in stackable plastic boxes called Living Walls.

A wishing well made from old tires has marigolds and pink geraniums growing out of the sides and top. Used wood is painted purple and makes up raised beds throughout the garden. Wood is also the foundation for the pool where tomatoes float. There's even a scarecrow made from discarded wire fence, egg cartons and tin pie plates, that hang off the arms to scare away four-footed scavengers.

Snap peas and leaf lettuce grow in 8-quart plastic bags of vermiculite, a peat-like growing substance. Actually, five alternative growing substances are represented in the bag culture garden, Toth said. Liter-sized plastic soft drink bottles have the bottoms cut off and are placed spout-end-in into the bags to act as funnels and provide support for young plants. "Bag culture is the cheapest way to garden," Toth says. All the gardener has to do is open the bag and plant a seed.

Urban gardeners who wish to invest some money, however, can purchase Living Walls in box and hanging-basket form at the Aboretum. They can be transformed into split rail fences, flowering gazebos or provide insulation when stacked against the outside of homes. The boxes range in size to hold anywhere from 13 to 79 plants that grow out the sides and top. Seeds are planted in 2 1/4 square inch windows and a growing medium of rockwool, vermiculite and oasis dust. The boxes not only save space but eliminate weeding and cultivating of the soil, Toth said. "Living Wall" baskets hang from trees and clotheslines with healthy tomato plants, bok choy (chinese cabbage), eggplant and strawberries. They are not cheap, however, costing from $23.95 to $87.50 each.

Some of Toth's garden themes are "yield gardens" producing $50, $100, $200 and $400 worth of produce. A large variety garden is filled with 14 different types of hot and sweet peppers and eight varieties of squash. There's a split rail herb fence. A third world garden demonstrates that crop farming in stacked cylindrical Living Walls uses one-tenth of the space of farming in the ground.

To date 1235 pounds of assorted vegetables have come out of the country garden this season. They are donated to the Capital Area Community Food Bank, which operates as a warehouse for 300 churches, soup kitchens and the Red Cross who feed hungry people in the Washington Area.

There'll be a lot more vegetables and herbs coming out of the country garden before this growing season is over, Toth said. The fall season is in full swing and he has just finished planting a whole new set of crops including broccoli, brussels sprouts, cauliflower and cabbage and snowpeas. In Washington there's still time to get in some lettuce, radishes, cress and spinach, but it's got to be planted today or the first frost will hit before there's time to harvest the crop, Toth said.

In the meantime, here are some recipes to use up what is already flooding our gardens, other than rain. GREEN AND RED TOMATO PUFF PASTRY SANDWICHES (6 servings) 17 1/2-ounce package frozen puff pastry Flour for rolling 2 large ripe red tomatoes 2 large ripe green tomatoes Salt and pepper, to taste 2 tablespoons fresh oregano (substitute 1 tablespoon dried) Dijon mustard, to taste 1/4 pound creamy havarti cheese, cut into thin slices and crumbled 1/4 pound genoa salami 1 egg, slightly beaten with 1 teaspoon water Defrost both sheets frozen puff pastry. Sprinkle a little flour on counter and rolling pin and roll pastry out about 1 inch longer and 1 inch wider. Split each sheet in half, to make four sheets. On two sheets make a layer of red and green tomatoes, alternating colors. Spread a thin mustard over the tomatoes, as you would for a sandwich. Sprinkle with salt, pepper and oregano. Divide the cheese and sprinkle over the tomatoes. Divide the salami in half and make an even layer over the cheese. Brush a little egg wash around the edges of the pastry. Top each with a remaining layer of puff pastry. Crimp the edges together and brush the top only with egg wash. Bake in a 350-degree oven for 30 minutes. MIXED VEGETABLE SALAD (10 servings) Small head cauliflower, cut into flowerets 2 small carrots 20 green beans 1 small zucchini, in 1/4-inch rounds 1 small yellow squash, in 1/4-inch rounds 10 cherry tomatoes 10 greek olives, pitted Bunch scallions, green part only

For the dressing: 1/3 cup red wine vinegar 1/2 cup olive oil 1 teaspoon dijon mustard 1 tablespoon dill 1 tablespoon chives Salt and pepper to taste 1 large clove garlic, finely minced

Steam cauliflower, carrots and green beans 4 minutes and plunge in cold water to stop the cooking. Steam zucchini and yellow squash 3 minutes and plunge in cold water. Rinse cherry tomatoes and cut in half. Cut olives in half and scallions in tiny rounds. Mix dressing ingredients and toss with vegetables. Let sit 30 minutes before serving so the vinaigrette seeps in, toss again and serve. COLLARD AND SORREL RICE ROLLS (4 servings) 1/3 to 1/2 pound ground lamb or country sausage 1 onion, finely chopped 1 1/2 cups cooked rice 1/4 teaspoon anise seed 1/4 teaspoon salt, if needed 1/2 teaspoon poultry seasoning (with lamb only) 8 large collard or chinese cabbage leaves 4 fresh sorrel leaves

Cook the meat and onion in a saute' pan, breaking the meat apart. Add the rice, anise seed, salt and optional poultry seasoning and mix well.

Dip the collard or chinese cabbage leaves in boiling water, holding on to the stem ends, until they are limp. Spread them on a work board, cut off the stems, and slit down the center rib of the leaf so it will roll easily. Tear or cut the leaves into pieces about 5 inches wide and 6 inches long (they can taper). Put 2 tablespoons of the rice mixture on bottom center of each leaf, put a 2-inch piece of sorrel leaf on top, and roll all this up in the leaf firmly, turning the sides in. Place the rolls tightly together on a steamer rack and stem for 15 minutes, uncovered, so they will keep their bright green color. From Lois Burpee's "Gardener's Companion and Cookbook"